Swift struct type recursion

Question

Why can\'t structs have recursive value types in Swift? Is this a temporary limit of the language or is it as intended?

I feel that the ability to declare a binary tree

Answer 1

Enums in Swift support recursive types using the indirect keyword so you can do something like:

indirect enum Tree<T> {

    case Node(left: Tree?, right: Tree?, element: T)

}

Check out this great blog post A persistent tree using indirect enums in Swift

Answer 2

The answer is in your question: structs are value types. If you include a substruct B into a struct A, it means, that one object of type A will have a size sizeof(all_other_fields_of_A) + sizeof(B). So, a value type can not be recursive: it would have infinite size.